1. Field of the Invention
The present invention is directed to stabilized aliphatic diperoxydicarboxylic acids and a process for preparing the same. The stabilized diperoxydicarboxylic acids are useful as bleaching agents.
2. Discussion of the Background
Peroxide compounds are used largely to bleach textiles, because in addition to their good bleaching action they are also cause negligible deterioration of the fabrics.
Sodium perborate has become very important at high washing temperatures since it is a safe and reliable, mild oxidant, and it yields good bleaching results. The drawback with this bleaching agent lies in the non-satisfactory bleaching action at low washing temperatures. The result of the sharp rise in the use of temperature-sensitive synthetic fibers and colored textiles, as well as the trend to conserve energy during the washing process is that, among other things, the significance of a low temperature bleach has increased, thus rendering the search for more active oxidants mandatory.
Peroxycarboxylic acids are suitable low temperature bleaching agents. Their drawback is the high tendency, in their pure form, to decompose exothermally or explode under thermal or mechanical stress so that safe handling without suitable safety measures is not possible.
Processes for safe handling have been developed, such as the preparation of the active bleaching peroxide compound in the washing liquor by reacting safe peroxide compounds (e.g. sodium perborate) with activators. However, these processes suffer from the drawback that there must be high concentrations of the starting peroxide compound and activator in order to compensate the loss of active bleaching species due to the sensitivity of the activators to hydrolysis, the susceptibility of the dosing to variations, and the varying rate at which the components dissolve (See A. Smith et. al., Low Temperature Bleach Systems, AOCS World Conference on Detergents, Montreaux, 1986).
In addition to this, due to the temperature-dependent velocity of the activation reaction, especially at low temperatures, the generation of sufficient concentrations of the active bleaching substance can be delayed, such delays being undesired.
Since these difficulties do not occur when peroxycarboxylic acids are added directly, researchers have tried for a long time to reduce the thermal and mechanical sensitivity of peroxycarboxylic acids by means of stabilization.
Among the available peroxYcarboxYlic acids, interest has focused on the longer chain aliphatic peroxycarboxylic acids, which contain less than 14% activated oxygen. Linear alpha, omega-diperoxydicarboxylic acids have especially preferred properties for general applications, since they have practically no intrinsic odor and good bleaching action even at temperatures ranging from 30.degree. to 40.degree. C. In addition to this, they have surface-active properties. Thus unlike perborate, they do not develop bleaching action everywhere in the washing liquor but rather specifically at the fabric. A systematic study of the bleaching action, published by Lieser et al. (Seifen, Ole, Fette, Wachse, 111, 452 (1985), based on the chain length, shows a maximum at C=12, i.e. for the diperoxydodecanedioic acid. Since the raw material dodecanedioic acid that is required to prepare diperoxydodecanedioic acid is also available on a large scale, the diperoxydodecanedioic acid has gained in importance.
To prepare water insoluble alpha, omega-diperoxydicarboxylic acids there exist various processes, whose basic principle, in accordance with DE-AS 10 48 569 is that the corresponding alpha, omega-dicarboxylic acids are converted with hydrogen peroxide using acid catalysts, usually sulfuric acid, in an aqueous medium at temperatures starting at -50.degree. C. The processes of U.S. Pat. Nos. 4,119,660, 4,244,884, 4,314,949, DE-OS 28 61 690, OS 32 01 579, OS 33 20 497 and OS 34 18 450, which also permit in part a continuous reaction, follow this same reaction principle. Usually suspensions containing 2 to 36% solids, whose liquid phase comprises 60 to 80% sulfuric acid in addition to residues of hydrogen peroxide, are obtained as the reaction product.
Further processing of the reaction product is also claimed in U.S. Pat. No. 4,119,660 and DE-OS 28 61 690. The insoluble diperoxydicarboxylic acid is removed by means of filtration, followed by a drying.
These processes suffer from the relevant drawback that during the process highly concentrated diperoxydicarboxylic acids occur that are extremely susceptible to mechanical and thermal strain. Thus these processes do not guarantee safe handling in technical scales.
In contrast, in DE-OS 33 20 496, OS 33 20 497 and OS 34 18 450, the acidic reaction product is neutralized immediately with alkali hydroxides so that there is a mixture of alkali sulfate and diperoxydicarboxylic acid which is separated out. However, the drawback is that due to the temperature and pH peaks in the alkaline region that occur during the neutralization a rapid decomposition of the peroxycarboxylic acids is brought about and thus high loss of the product occurs.
Thus to date there exists no process that permits the further processing of diperoxydicarboxylic acid suspensions, obtained during peroxygenation, in a safe manner without significant loss of the active substance.
Since peroxycarboxylic acids cannot such be safely handled in their pure form, these bleaching agents must be stabilized.
Thus it has been known for a long time that according to BE-PS 560 389, peroxycarboxylic acids can be transmitted to an adequately stabilized, safely manipulable form by mixing with hydratable inorganic salts, in particular sodium sulfate and magnesium sulfate. Numerous methods have been developed to carry out the mixing process. Thus DE-OS 20 38 833 proposes performing the stabilization of aqueous, frozen peroxycarboxylic acid droplets in a fluid bed of magnesium sulfate so that the peroxycarboxylic acid suspension is surrounded by a salt hydrate.
In contrast, the DE-OS 24 22 735 describes processes in which the dry or almost dry peroxycarboxylic acid is blended by mechanical means with the salt chosen as the stabilizator.
Another problem area with peroxycarboxylic acids is their poor chemical stability during storage. The presence of heavy metal ions, which are known as extremely effective decomposition catalysts for peroxides, was postulated as the cause for the poor chemical stability (see R. Criegee in Houben-Weil, Vol. 8, 1952).
To improve the chemical stability, DE-AS 11 74 755, AS 12 80 239 and DE-OS 29 38 731 and OS 22 14 500 propose adding complexing agents as additives for heavy metals such as quinaldine acid, quinoline, polyphosphates, aminophosphoric acids and EDTA. By these measures end products with improved, yet still unsatisfactory chemical stability are obtained.
In order to design the stabilization of peroxycarboxylic acids with sodium sulfate such that the process is economically feasible and in order to largely avoid the disposal problems of sulfuric acid or sodium sulfate solution, it is logical to generate the sodium sulfate required for the stabilization essentially from the process sulfuric acid that is obtained. Therefore, DE-OS 36 28 263 proposes treating the reaction mixtures that are prepared e.g. according to DE-OS 33 20 497 with a purified sodium sulfate that is recovered from a recycled waste liquor and preferably present as a saturated aqueous solution, then neutralizing the mixtures obtained with the sodium hydroxide solution, and finally separating the peroxycarboxylic acid, stabilized with sodium sulfate, from the mother liquor.
Pure sodium sulfate, which is recycled preferably as an aqueous solution into the reaction mixture obtained, is recovered from the mother liquor, which is saturated with sodium sulfate, by means of crystallization. In this process it is absolutely necessary to remove almost all of the impurities in the inhibited peroxycarboxylic acids. To achieve this, primarily the traces of heavy metals, which are especially critical in this method, must be largely discharged by means of the sodium sulfate-containing mother liquor, whereby the heavy metal concentration in the recycled sodium sulfate may be no more than 5 ppm and in the end products in general no more than 2 ppm. This process reduces, of course, the quantity of sodium sulfate-containing waste liquor, yet inhibited peroxycarboxylic acids are obtained that despite an extremely low impurity content, in particular the content of heavy metals, exhibit no improved stability in storage. In addition, on the one hand it is technically expensive to almost completely remove impurities in the ppm range; and on the other hand, a drawback also exists in the risk that with fluctuations in the quality of the added materials or process failures a non-tolerable level of impurities can be very rapidly reached, which in turn leads to drawbacks with respect to the stability in storage and safe handling.
However, in addition to problems concerning safe handling and chemical stability, peroxycarboxylic acid formulations are subject to still other requirements. Since the primary field of application for peroxycarboxylic acids is the bleaching of textiles, peroxycarboxylic acid formulations blended with detergents must have properties that match the conventional components of detergents. To guarantee good flowability and to avoid separation processes in the detergent it is beneficial to use the solid peroxycarboxylic acid formulations at a particle size ranging from 200 to 1250 microns and at bulk densities ranging from 400 to 800 g/l. This specification profile can in principle be attained by agglomeration granulation.
Thus the DE-OS 35 15 712 and the EP-A 256 443 describe processes for granulating in which solid, stabilized peroxycarboxylic acids are agglomerated using a water soluble polymer as the granulating aid. In this process the agglomeration is achieved by spraying an aqueous solution of the granulating aid on the agitated, stabilized peroxycarboxylic acid. According to DE-OS 35 15 712 granulating is also achieved by means of dry blending the granulating aid with the inhibited peroxycarboxylic acid and then spraying with water. A similar process is claimed by the GB-PS 8 127 157 in which polyvinyl alcohol and derivatives are used preferably for granulating in a fluid bed.
By these measures agglomerates can be manufactured according to specification. According to H. Telschig (Seifen, Ole, Fette, Wachse, 1984, 1), however, it is known that the bulk densities of the end products are determined essentially by the bulk density of the starting products. Thus in normal cases a 5 to 10% reduction in the bulk density can be achieved by agglomeration in exceptional cases up to 17%. However, granules with low bulk densities can be manufactured only if initial products with a corresponding low bulk density are available.
Even though a number of problems are solved by means of the described measures, to date there are no sufficiently storage-stable and safe to handle peroxycarboxylic acid formulations, which can be safely prepared and whose specifications correspond to the conventional components of detergents. In addition to this, the use of process sulfuric acid or sodium sulfate that is prepared therefrom for stabilization has not been satisfactorily solved as yet.
A need continues to exist for a safe and unobjectionable process and for improved diperoxydicarboxylic acid granulates, which do not exhibit the drawbacks of the prior art methods and products, and which permits the use of process sodium sulfate.